EP0186312B1 - Purification of bayer process liquors - Google Patents

Purification of bayer process liquors Download PDF

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Publication number
EP0186312B1
EP0186312B1 EP85308537A EP85308537A EP0186312B1 EP 0186312 B1 EP0186312 B1 EP 0186312B1 EP 85308537 A EP85308537 A EP 85308537A EP 85308537 A EP85308537 A EP 85308537A EP 0186312 B1 EP0186312 B1 EP 0186312B1
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EP
European Patent Office
Prior art keywords
liquor
slurry
process according
ammonium salt
solids
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Expired
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EP85308537A
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German (de)
English (en)
French (fr)
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EP0186312A2 (en
EP0186312A3 (en
Inventor
John T. Malito
William J. Roe
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Kaiser Aluminum and Chemical Corp
ChampionX LLC
Original Assignee
Kaiser Aluminum and Chemical Corp
Nalco Chemical Co
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Publication of EP0186312A2 publication Critical patent/EP0186312A2/en
Publication of EP0186312A3 publication Critical patent/EP0186312A3/en
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
    • C01F7/47—Purification of aluminium oxide, aluminium hydroxide or aluminates of aluminates, e.g. removal of compounds of Si, Fe, Ga or of organic compounds from Bayer process liquors
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
    • C01F7/47—Purification of aluminium oxide, aluminium hydroxide or aluminates of aluminates, e.g. removal of compounds of Si, Fe, Ga or of organic compounds from Bayer process liquors
    • C01F7/473—Removal of organic compounds, e.g. sodium oxalate
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/84—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by UV- or VIS- data

Definitions

  • Alumina trihydrate the precursor of many alumina-based products, including calcined alumina used for making metallic aluminum by reduction, is most commonly obtained from alumina-containing ores, such as bauxite.
  • Recovery of the alumina content of bauxite is generally accomplished by the well-known Bayer process which involves the digestion of the bauxite with a caustic medium at elevated temperatures and pressures. Digestion of the bauxite results in a saturated sodium aluminate liquor, commonly referred to as "pregnant liquor” from which the alumina content is recovered by precipitation, usually through addition of seed alumina.
  • pregnant liquor saturated sodium aluminate liquor
  • Bauxite is found in many parts of the world and the composition of the ores may vary from place to place.
  • organic impurities Many bauxites contain organic impurities and these organic impurities will be co-extracted with the alumina content of the ore during digestion and will contaminate the produced liquor.
  • Most of the organic impurity content found in the ores consists of high molecular weight compounds, such as humic acids, a portion of which will decompose to lower molecular weight compounds during the caustic digestion process, thereby producing a whole spectrum of organic salts dissolved in the liquour.
  • a part of the organic impurities dissolved in the liquor consists of color-causing compounds, such as humates, and, consequently, the pregnant liquor will usually possess a dark red color.
  • the formation of a precipitated hydroxide mixture creates operational difficulties.
  • the precipitated hydroxide mixture will contain aluminum hydroxide and this results in product alumina loss; on the other hand, the precipitated mixture has to be separated from the rest of the treated liquor and this involves additional processing steps and/or a definite increase in the quantity of the total mud load which requires disposal.
  • U.S. 4,101,629 Mercier et al
  • a barium-containing compound is added to Bayer process liquors.
  • the barium compound precipitates as barium aluminate and the precipitated material may also include barium salts of organic impurities present in the liquor.
  • this process involves precipitation of a compound which has to be removed from the treated liquor requiring settling and/or filtration equipment and additional processing steps.
  • the process allows recovery and reuse of the filtered barium compound by calcination; however, the well-known toxicity of barium salts may create An unacceptable environmental and/or health risk not justifiable by the purification results obtainable by it.
  • sodium oxalate one of the organic impurities in Bayer liquor, is removed from spent Bayer liquor.
  • dissolved sodium oxalate is removed from spent Bayer liquor by addition of a cationic sequestrant to the spent liquor.
  • the cationic sequestrant preferably a simple quaternary nitrogen compound possessing medium and long-chain alkyl groups and a single cationic charge, produces an insoluble product with humic compounds present in the liquor, thus destabilizing the spent liquor with respect to sodium oxalate. Destabilizing allows precipitation of a portion of the oxalate impurity content.
  • the insoluble sequestrant-humic acid product will form an oily scum on the surface of the spent liquor and cannot be readily removed from the spent liquor. Elimination of the oily layer from the surface of the liquor cannot be done by conventional filtration. It has to be accomplished either by equipment adapted for this particular purpose or by using a filtration method capable of dealing with semicolloid surface layers. Consequently, the difficulties associated with the process render it impractical.
  • U.S. 4,335,082 suggests the removal of organic impurities from impure Bayer liquors by caustifying the liquor with lime, followed by evaporation of the causticized liquor. Evaporation will result in the precipitation of solids containing a large quantity of the organic impurities from the liquor. The solids are separated and then discarded. This method assures the removal of satisfactory quantities of organic impurities from the liquour but the problems associated with the process render it impractical and expensive. To achieve good purification, large volumes of liquor have to be treated with lime and evaporated. These involve large quantities of lime and extensive energy input. Also, by treating large volumes, large losses of soda values can be expected.
  • the present invention thus provides a process for removing from a Bayer process liquor or slurry coloured materials present therein, characterised in that a water-soluble cationic polymeric quaternary ammonium salt is brought into contact with solids which are to be added to the Bayer liquor or slurry or are generated in dispersion in the liquor or slurry by the Bayer process, the resultant coacervated adduct contacts the liquor or slurry, and the coacervated adduct is removed from the liquor or slurry.
  • the dispersed solids may be, for example, red mud particles, alumina trihydrate, or oxalate salts. If they are added, they may be, for example, various filter aids.
  • Treatment of the solids with the cationic polymeric quaternary salt provides an adhered surface coating or layer on the dispersed solids, and this coating or layer creates a receptive surface for the humates present in the Bayer process liquor.
  • the adduct contains the dispersed solid, the cationic polymeric quaternary ammonium salt and the humate impurities, all bound into a coacervate adduct by adsorptive and/or chemisorptive forces.
  • these coacervated adducts are dense precipitates which are easily removed from Bayer process liquors and slurries by standard separation techniques such as filtration, flocculation, settling and the like.
  • the coacervate adduct may thus be formed by first coating the solids with the polyquaternary salt, or surprisingly may also be formed in situ by adding effective amounts of the polyquaternary salts to humate contaminated liquors in the presence of the solids normally present in these liquors or added to these liquors to improve filtration characteristics.
  • humates is used in this specification to mean any of the colored materials present in Bayer process liquors. Such materials include not only salts of humic acid but also lignin derivatives.
  • Figure 1 graphically shows the humate removal efficiency of the polymeric quaternary ammonium salt when applied to precalcination filter feed alumina hydrate as a function of ammonium salt concentration in mg per liter of Bayer process liquor at a predetermined hydrate concentration.
  • Figure 2 graphically depicts the humate removal efficiency of the polymeric ammonium salt when applied to press feed liquor as a function of ammonium salt concentration per liter of Bayer process liquor.
  • Figures 3 graphically shows the humate removal efficiency of the polymeric ammonium salt when applied to red mud containing slurries.
  • This invention relates to the purification of Bayer process liquors, and more particularly it concerns a process for the removal or at least reduction of the organic impurity level of Bayer process liquors.
  • Bayer process liquors or “liquor” relate to any caustic liquor which is generated in the Bayer process or is used to dissolve alumina values from bauxite.
  • Typical examples of Bayer process liquors include pregnant liquor, spent liquor, washer underflow, and slurries containing precipitated alumina hydrate, as well as the liquor containing dispersed red mud particles. All of these liquors have varying caustic contents and contain organic impurities.
  • organic impurity or "organic impurities” refer to organic matter present in Bayer process liquors, the type and quantity of which varies considerably with bauxite source and Bayer plant operating conditions.
  • the greater part of the organic impurities is present as the alkali salts of organic acids which are colorless and, apart from the oxalate content, present only a minor problem from the viewpoint of the quality of the alumina trihydrate produced from the liquor.
  • Process conditions and alumina hydrate quality are significantly affected by portions of humates. These colored materials are of uncertain composition and possess complex structures.
  • This stabilizing effect of the humates keeps the lower molecular weight organic impurities in solution until over-saturation concentration is reached or exceeded, uncontrollable precipitation of these lower molecular weight compounds, particularly fine oxalates, can occur during precipitation of alumina hydrate and the co-precipitated oxalate can seriously interfere with the production of satisfactory alumina hydrate.
  • the oxalate can coat the produced hydrate, requiring extensive washing operations to remove the adhered oxalate from the hydrate surface.
  • the precipitated oxalate can cause nucleation of alumina hydrate resulting in the formation of very finely distributed hydrate which due to the small particle size will not meet product standards.
  • the oxalate can also precipitate on the surface of alumina hydrate seed added to pregnant liquor for the production of alumina hydrate, thus preventing precipitation of the desired product hydrate.
  • uncontrolled precipitation of the oxalate can cause serious scaling of process vessel walls resulting in reduced heat-transfer efficiency and additional labor involved in the removal of the scale.
  • control of the humate content of Bayer process liquors is of paramount interest if a satisfactory alumina hydrate is to be produced in an efficient and economic manner.
  • the present invention is directed to a control of the humate content of Bayer process liquors. This goal is achieved by removal or at least significant reduction of humate content by treating Bayer process liquors containing humates in the presence of dispersed solids with a water-soluble, cationic, polymeric quaternary ammonium salt.
  • the dispersed solids can be the type generated by the Bayer process, for example, red mud particles, alumina trihydrate or hydrate, and oxalate salts.
  • the dispersed solids also include various filter aids which are generally incorporated in the liquor prior to filtration. Such filter aids may include certain calcium compounds, for example, calcite, aragonite, or hydrated calcium aluminate which enhance the filtration step.
  • the dispersed solids may also include pretreated filter aids or pretreated seed crystals which are added to the Bayer process prior to reaction with the water soluble cationic polymeric quaternary ammonium salts of this invention, thereby forming a solid-polyquaternary salt adduct, which adduct may then be advantageously added to Bayer process liquors to remove humates and color bodies.
  • filter aids may be precoated with the polyquaternay salts prior to being used to precoat the filters used to remove colloidal matter prior to seeding and crystallizing aluminum trihydrate.
  • the preferred water-soluble, cationic, polymeric quaternary ammonium salt employed in the present process is a polydiallyl dimethyl ammonium chloride (POLYDADMAC) compound containing the monomer diallyl dimethyl ammonium chloride (DADMAC) which has the following chemical structure.
  • POLYDADMAC polydiallyl dimethyl ammonium chloride
  • DADMAC monomer diallyl dimethyl ammonium chloride
  • Polymerization of this monomer may be accomplished by standard vinyl polymerization techniques, but is preferably completed by free radical initiation of this vinylic monomer, in the presence or absence of other vinylic monomers such as acrylamide, methylacrylate, and the like. Polymers of this type are described in Butler, U.S. 3,288,770. Polymerization may be accomplished with the DADHAC monomer alone, leading to homopolymers, or with DADHAC and other vinylic monomers, leading to DADMAC containing copolymers. Such copolymers are illustrated in Table I.
  • the preferred POLYDADMACS to be used in this invention are homopolymers/DADMAC and have an intrinsic viscosity of at least 0.1 and preferably have an intrinsic viscosity ranging between about 0.3 to about 1.0.
  • POLYDADMAC may also refer to other vinylic polymers containing DADMAC monomer, such as copolymers of DADMAC and acrylamide.
  • the Intrinsic Viscosities are at least 0.2 and may range as high as 1.5 or above.
  • intrinsic viscosity refers to the viscosity-molecular weight relationship as described in detail in chapter IV of "Polymer Handbook", Edited by J. Brandrup and E. H. Immergent, Published by Interscience Publishers, New York, 1966.
  • POLYDADMAC water-soluble, polymeric cationic quaternary ammonium salt utilized in the present invention to accomplish the purification of the Bayer process liquors.
  • Table I describes other types of polyquaternary salts which function in this invention, however, the scope of the invention is not limited thereto, since it is expected that other polyquaternary salts which can tolerate the pH extremes of the Bayer process will also function to remove humates.
  • the flocculation of the mud in the settler(s) and washers is achieved with the aid of either naturally occurring settling aids, such as starch, or any of the commercial synthetic flocculants suitable for red mud. It was found that effective removal of humates is accomplished by addition of POLYDADMAC directly to the red mud slurry prior to treatment with flocculants and charging to the settler(s).
  • the concentration range of POLYDADMAC per liter of slurry treated is within the range from about 1.0 mg to 500 mg and preferably within the range from about 2.0 mg to 40 mg depending upon the solids concentration of the slurry.
  • the POLYDADMAC is added as an aqueous solution containing from 10 to about 50 weight % active polymer.
  • the required quantity of POLYDADMAC is applied to the mud slurry from an aqueous solution, however, spent liquor may also be used as a dispersing medium.
  • Contact of the humate-containing liquor with the polyquaternary coated mud results in at least a reduction of the humate content of the liquor which can be readily observed by a change in the color of the treated liqour.
  • Quantitative determination of humate removal can be achieved by well-known colorimetric methods using a conventional colorimeter. It was discovered that when the POLYDADMAC quantity applied to the mud slurry is within the broad range shown above, reduction in humate content (as determined colorimetrically) can range from about 7% to more than about 50%. The humates removed from the liquor are adhered or bound to the mud and are discarded together with the mud discharge, thus providing a convenient way of disposal. Alternatively, POLYDADMAC can be added to any of the red mud slurry streams which feed into the mud washers.
  • humate is removed from press feed liquor.
  • the pregnant liquor charged to the press feed tank still contains suspended solids which have to be removed prior to subjecting the pregnant liquor to seeded precipitation.
  • Removal of the suspended solids is generally accomplished by filtration in the presence of filter aids, such as certain calcium compounds.
  • filter aids such as certain calcium compounds.
  • Kelly-type filters are employed and the filters can be coated with a calcium-containing filter aid which allows efficient filtration of the pregnant liquor-containing suspended solids. It was found that effective removal of humates can be accomplished by introducing the POLYDADMAC into the filter aid slurry prior to the subsequent mixing of the filter aid with the press feed liquor. Coating of the surface of the filter aid accomplished two purposes.
  • the treating agent on the surface can be assured; on the the other hand, good contact with the humate-contaminated liquor can be achieved.
  • the treating agent can be introduced into the press feed liquor after the dispersion of the POLYDADMAC is assured.
  • any other type of filter can be equally utilized in the treatment, and in lieu of the calcium-containing filter aid, other types of filter aids, such as cellulosic materials, can also be employed.
  • the quantity of POLYDADMAC to be applied to the filter aid surface for achieving humate removal is relatively small.
  • concentration range of POLYDADMAC per liter of liquor treated is within the range from about 1.0 mg to about 400 mg and preferably within the range from about 2.0 mg/l to about 50 mg/l.
  • the required quantity is applied to the surface of the filter aid from an aqueous solution; however, spent liquor may also be used as a dispersing medium.
  • Contact of the humate-containing liquor with the POLYDADMAC-coated filter aid results in a reduction of the humate content of the liquor which can be readily observed by a change in the color of the filtrate liquor. Quantitative determination of humate removal is accomplished as previously described.
  • reduction in humate content can range from about 8% to more than about 55%.
  • the humates removed from the liquor are adhered or bound to the filter aid and are discarded together with the used filter aid, thus providing a convenient way of disposal. If the filter aid is regenerated, for example, by calcination of the calcium-containing used filter aid, the humates are destroyed during calcination and the regenerated filter aid can then be reused without danger of being contaminated or causing contamination.
  • the removal of humates from Bayer process liquor is accomplished during the hydrate filtration stage of the Bayer process.
  • the hydrate filtration stage of the Bayer process consists of filtering precipitated and, if desired, washed alumina hydrate.
  • the filtered hydrate is then subjected to calcination to convert it to reduction-grade alumina oxide.
  • the resultant filtrate from the filtration step is usually recycled to the Bayer process.
  • This alumina hydrate slurry contains humates which, if not removed, would be recycled to the Bayer process.
  • removal of the humates in this filtration stage would prevent or, at least, reduce accumulation of humates through recycle of the filtrate.
  • humates can be successfully removed from the alumina hydrate slurry by introducing POLYDADMAC into the slurry to be filtered.
  • Introduction of the POLYDADMAC into the slurry is suitably accomplished by coating the surface of alumina hydrate with the POLYDADMAC and charging the coated hydrate into the slurry.
  • the treating agent may also be introduced into the slurry itself without precoating alumina hydrate and if good dispersion of the treating agent in the slurry is assured, then the POLYDADMAC will uniformly coat the surface of the alumina hydrate present in the slurry. The coated hydrate will allow removal of the humates from this slurry by the contact of the surface adhered POLYDADMAC with the humates.
  • the quantity of POLYDADMAC to be added to the slurry is within the range from about 2.5 mg to about 400 mg per liter of slurry. Optimum results in terms of humate removal can be achieved when treating agent quantities within the range from about 10 mg to about 150 mg per liter of slurry are applied.
  • the measure of humate removal is conveniently determined by colorimetric methods which involve measuring the reduction in color of the filtrate against a filtrate obtained from an untreated slurry. When POLYDADMAC quantities referred to above are utilized, color reductions from about 10-60% can be achieved.
  • the humates removed from the slurry will be on the surface of the filtered alumina and will be destroyed during calcination. Consequently, there is no need for purifying the hydrate or for providing disposal means required by prior art processes.
  • Humate removal was accomplished from a Bayer process liquor containing precipitated alumina hydrate solids.
  • the liquor or slurry employed in the instant purification process was a characteristic alumina hydrate slurry commonly used as feed to hydrate filters preceding the calcination stage of the Bayer process.
  • the filtered hydrate is charged directly to the calciners for conversion to reduction-grade alumina (Al2O3) while the filtrate is recycled to the Bayer process.
  • the slurry utilized in this example had an average solids concentration of 50.7% by weight, a temperature of about 58 o C (137 o F) and this slurry was pumped to a conventional filter at an average rate of 1041 l/min (275 gpm).
  • the treating agent POLYDADMAC
  • POLYDADMAC was introduced as both a 20% active solution, as well as a dilution of the 20% active product, to allow comparison as far as surface coating of the hydrate and humate removal efficiency was concerned.
  • Introduction of the POLYDADMAC was at the suction side of the pump feeding the slurry to the filter.
  • the quantity of the treating agent was varied.
  • the humate removal efficiency was established by colorimetric means which involved measuring the absorbance of the liquor phase prior to addition of the POLYDADMAC and the absorbance of the filtrate.
  • Humate removal from Bayer process liquor obtained after separation of the red mud residue through settling was practised.
  • the pregnant liquor, as received from the mud settler overflow, was treated with POLYDADMAC prior to filtration aimed at removal of residual dispersed red mud particles.
  • the pregnant liquor also called “press feed”, due to the conventionally employed Kelly press filters for such solids removal, is generally filtered in the presence of a solid filter aid which significantly improves the filtration efficiency. Addition of the POLYDADMAC was accomplished in a manner to allow utilization of the solid filter aid as a "carrier” for the cationic polymeric treating agent.
  • solution POLYDADMAC product (20% active) dosages of 18, 31, and 57 mg/l of press feed were employed.
  • the POLYDADMAC treating agent was at first diluted with water to concentrations corresponding to 194, 324, and 302 mg/l, respectively, prior to charging to the press feed.
  • the POLYDADMAC-containing press feed was then filtered on conventional press filters which had a filter aid precoat prior to contact with the POLYDADMAC-containing press feed.
  • Humate removal was determined by measuring the absorbances of the filtrates obtained and the absorbances of the untreated press feed. The humate removal results are shown in Table III and in Figure 2.
  • Tests were also conducted to establish the effectiveness of POLYDADMAC in the removal of humates from digested Bayer process slurries, the slurries being treated prior to the separation of the red mud by settling.
  • Settler feed slurry having a temperature in the range from about 90-99 o C (194-210 o F) was contacted with varying dosages of the 20% active POLYDADMAC solution and the absorbances of the treated slurry, after removal of the red mud, were compared to the absorbance value obtained from the untreated slurry.
  • Table IV The results of the test are shown in Table IV and also in Figure 3.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Separation Of Suspended Particles By Flocculating Agents (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
EP85308537A 1984-12-27 1985-11-25 Purification of bayer process liquors Expired EP0186312B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US686803 1984-12-27
US06/686,803 US4578255A (en) 1984-12-27 1984-12-27 Purification of Bayer process liquors

Publications (3)

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EP0186312A2 EP0186312A2 (en) 1986-07-02
EP0186312A3 EP0186312A3 (en) 1988-05-25
EP0186312B1 true EP0186312B1 (en) 1991-08-28

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US (1) US4578255A (https=)
EP (1) EP0186312B1 (https=)
JP (1) JPS61174113A (https=)
CN (1) CN1007422B (https=)
AU (1) AU555168B2 (https=)
BR (1) BR8506493A (https=)
CA (1) CA1236680A (https=)
DE (2) DE3583930D1 (https=)
ES (1) ES8703531A1 (https=)
HU (1) HU200305B (https=)
IE (1) IE58328B1 (https=)
SU (1) SU1563589A3 (https=)
YU (1) YU44278B (https=)

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EP0186312A2 (en) 1986-07-02
CN1007422B (zh) 1990-04-04
EP0186312A3 (en) 1988-05-25
AU3863185A (en) 1986-07-03
DE186312T1 (de) 1986-11-06
US4578255A (en) 1986-03-25
IE853311L (en) 1986-06-27
CA1236680A (en) 1988-05-17
HU200305B (en) 1990-05-28
IE58328B1 (en) 1993-09-08
CN85109376A (zh) 1986-08-27
HUT39404A (en) 1986-09-29
DE3583930D1 (de) 1991-10-02
JPS61174113A (ja) 1986-08-05
SU1563589A3 (ru) 1990-05-07
BR8506493A (pt) 1986-09-02
AU555168B2 (en) 1986-09-11
JPH0149645B2 (https=) 1989-10-25
YU203985A (en) 1987-12-31
ES8703531A1 (es) 1987-02-16
YU44278B (en) 1990-04-30
ES550419A0 (es) 1987-02-16

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